Electromagnet with plunger



Feb. 10, 1948. E. R. BOYNTON Erm. 2,435,817

ELECTROMAGNET WITH PLUNGER Filed sept. so, 1944 mi .iis

Inventors: Erwin RBoynton., Wil Ham lauch, b '7E/M:

'y'lher` Attorney.

iiatented Feb. 10, 1948 UNITED STATES PATENT OFFICE ELECTROMAGNET WITH PLUNGEB Erwin R. Boynton, Schenectady, and William T. Rauch, Pattersonville, N. Y.. signora to General Electric Company, a corporation of New York Application September 8l, 1944, Serial No. 556,535

3 Claims. 1

disc of thin spring metal which has been cut away to form a plurality of narrow strips or spokes supporting each end of the armature. These spokes are arranged to bias the armature normally in an axially displaced unattracted position. Upon energization of the coil, the armature is moved against the bias force of the spokes to an attracted position, the movement of the amature being substantially proportional to the change in current in the coil.

For a more complete understanding of our invention, reference should be had to the accompariyingl drawing, Fig. 1 of which is a plan view partly in section showing the application of two eiectromagnets embodying our invention to the operation of a hydraulic valve; Fig. 2 is an enlarged view in perspective oi.' a spring support for one end of the armature; Fig. 3 is an enlarged sectional view of an electromagnet embodying our invention taken along the line 3-3 of Fig. 4 looking in the direction oi the arrows; while Fig. 4 is an end view of an electromagnet embodying our invention.

Referring to the drawing, We -provide an operating coil I wound on a spool 2 of electrically insulating material with annular washer-shaped members 3 and 4 at its opposite ends joined by a ring 5 surrounding the coil, which parts form a support for the coil. Also, these parts are made of a magnetic material and form a magnetic circuit for the coil which is complete, except axially through the coil.

Extending axially through the coil, we provide a plunger armature comprising an outer tubular member 8 provided on its opposite ends with ridges or flanges I and 8, the cylindrical peripheral surfaces of which form pole faces with respect to the stationary -pole faces constituted by the inner edges 9 and Ill of the members 3 and I. The armature is mounted at each end on a disc-like spider supporting member I I, shown in detail in Fig. 2. This member is constructed from a disc oi thin nonmagnetic spring metal of sufficient thickness to have the desired spring force, with three segmental sections cut away to leave three radially extending spring strips or spokes I2, I! and Il connecting hub portion Il with the outer annular portion. For the purpose of increasing the resiliency of the spokes, each of them is provided with a substantially central arcuate bend indicated on the spoke I2 by the reference numeral I 2a, the displacement of the bent portion beingrat right angles to the plane yci' the support II. In a typical device the spider f.' supports were made of phosphor bronze material 22,013" thick.

` As shown in Fig. 3, the armature is secured at each end to a support by means of a, tube Il which extends through the member 6, both of which are made of magnetic material, and has each end extending through an aperture in the hub portion of a support II or IIa. A flange is provided on each end of the tube I6 on the outer side oi' the hub, whereby the hub is secured against the end of the member 6. This construction may be eiected by providing a flange on one end only of the rod I6, assembling the parts and then upsetting the other end of the tube I6 to form the flange at that end.

The two spider supports II and IIa and the other parts are secured together by means of a plurality of bolts Il, six being shown, which bolts extend in parallel relation with the axis of the coil and through the ring members 3 and l. Also, the bolts extend through an end cap member Il enclosing one end of the solenoid and through a spacing ring I 9 at the other end of ,the solenoid. In the construction shown, this spacing ring I9 is seated against a, wall 20 of a supporting member provided with tapped holes into which the screws I1 extend, whereby the assembly is secured together and secured to the support 20.

As shown in Fig. 3, the annular pole flanges l and 8 are positioned on the plunger armature l so as to be biased by the spider supports axially toward the left hand to unattracted positions. Thus, when the coil is energized, a magnetic force is applied to the armature which moves thc armature toward the right against the spring bias of the spider supports. The pole anges 1 and 8 are moved to positions nearly opposite the pole faces 9 and In by maximum energization of the coil, this being the fully attracted position.

It will be understood that the magnetic force applied to the armature 8 in an axial direction toward the right would be zeroif the armature were moved toward the right far enough to bring the pole flanges 1 and 8 exactly opposite the pole faces 9 and IB or, in other words, in alignment naar? 3 with -the pole iaces I and Il. Thereicre, the biasing forces applied by the spider supports prevent the armature from reaching this position of complete alignment. For a given excitation o! the coil, the magnetic force applied to the armature decreases as the amature is moved toward this position or pole face alignment. As a result, the amature has a definite stable position for each value of coil excitation up to its iinai attracted position of near alignment oi the pole faces.

'I'his is a distinguishing characteristic of our electromagnet as contrasted, for example, with conventional solenoids such as those having a pivoted or plunger type armature in the operation of which the armature, when it starts to move toward its attracted position. the excitation being constant. is pulled with an increasing magnetic force. Such armatures obviously do not have a stable position for each value of excitation because when the excitation is made great enough to start movement oi' the armature against its biasing force, the increasing magnetic force moves the armature immediately to its fully attracted position.

As shown in Fig. 3, the armature I is positicned by the spider supports il and ila, the coil being deenergized, in an unattracted position with the pole flanges l and I axially on the letthand side of the pole faces i and Il. In this unattracted position, it will be understood that the spider supports assume their normal shapes and hold the armature in a position in which neither one exerts a spring bias on the armature. unless the amature is prevented from assuming that position, although movement of the armature toward the right hand to an attracted po. sition is immediately opposed by the spring biasing forces oi' the spokes or arms of the spider supports tending to return the armature to the unattracted position shown in Fig. 3.

When the coil is energized, a magnetic force is applied to the armature in a direction to move it toward the right hand, this f orce varying with the excitation current supplied to the coil. 'I'he axial range of movement of the armature is relatively small, and the bends i2 in the spokes of the spider supports provide the necessary elongation of the spokes required for this movement. In the unattracted position of Fig. 3, the spokes have their'minimum lengths, the hub il of each spider then lying in the plane of the peripheral ring portion of the spider. We have found that the armature movement is closely proportional to the current in the coil throughout its range of movement. Consequently, by suitably varying the current, a very small movement of the armature can be obtained between the unattracted and attracted positions, This proportional, or substantially straight line, relation between the movement oi' the armature and the current in the coil is, we have found, dependent to a considerable extent upon the bends I2 in the spider supports whereby the spokes are given greater resiliency.

An important feature of our invention in the provision of the substantially straight line current-displacement relation is the elimination oi all bearings for the armature with their inherent static friction which would tend to prevent movement of the armature in responseto very small changes in the excitation current. The pole ilanges 1 and 8 are suiiiciently smaller than the pole faces 9 and I0 to provide for a predetermined radial clearance or air gap between them sumcient to neutralize -the residual inthecorepartsaitertheeoilhnbeendeenergized. Another important ieatureisthee tionoianypositionotaeroairgapiortbearmature with incidental sticking in auch position.

We contemplate in one application ot our invention. as shown in Fig. l. the use of two electromagnets 2i and 22 constructed, as previously described, for operating jointly the plunger valve member 23 ot a hydraulic valve 2l. Thus the magnets 2i and 22 are molmted on a hydraulic valve casing with their armatures bearing respectively on opposite ends of the plunger member 23. To facilitate the adjustment of the armatures in engagement with the plunger, we provide each armature, as shown in Fig. 3. with a threaded bolt 2l extending through a longitudinal hole in the tube il, which hole has a portion threaded and cooperating with the threads on the bolt 2l. Thus by removing a cap 2l in the end cover il, access is had to the left-hand or outer end of the bolt 2l, which can be turned for longitudinal adjustment into engagement with the end oi the plunger 2i. It is secured in its adjusted position by a nut 21 and lock washer.

Preferably, as shown in Fig. 1, the adjustment oi' the two armatures issuch that the plunger 23 is held in a central closed position, as shown, by the Opposed biasing forces of the supporting spiders when the two electromagnets are deenergized. The adjustment bolts 2l are screwed against the opposite ends of the plunger 2l to apply a small amount of force to the plunger so that the supporting spiders are placed under some initial tension for Positive positioning oi the plunger 22 when the coils are deenergized. Thus energization. of the magnet 2| moves the plunger 23 toward the right hand and energiza.- tion of the magnet 22 moves it toward the left hand. Preferably, however, the two magnets are diierentially energized so as to provide for a magnetic restoring force in addition to the spring bias of the spider supports. In other words, the two electromagnets would both be partially energized at the same time. When these energizations are equal, the armatures are in their unattracted positions into which they were moved by the combined spring bias of the spider supports and the opposing magnetic forces applied to the armatures as the energizations oi' the coils were equalized. Thus any force tending to displace the valve plunger 2l, such as resulting from a heavy shock, is opposed not only by the spring biases but also by the magnetic forces. For movement oi the plunger toward the right hand, as seen in Fig. l, the energization in the magnet 2| is increased while the energization in the magnet 22 is decreased, and vice versa.

It the armature is held in a nxed position. it exerts a force which is proportional to the square of the current. The amount of force increase for a given current increase decreases as the saturation of the iron core of the electromagnet is approached. However, we contemplate that the electromagnet will be operated below the saturation point. The biasing force exerted by the spider supports, however, are not exactly proportional to the movement of the armature. In a typical installation, as shown in Fig. l, it was found that with the two electromagnets excited to about one-half of their maximum values when the valve was in its central closed position shown, the movement of the valve was substantially proportional to the changes in the excitations of the electromagnets. In other words, the travel of the valve was nearly proportional to the difference in the excitations of the two coils.

As indicated in Figs. 1 and 3, the fluid of the valve 24 has access to the interiors of the electromagnets around the armatures and the spider supports. This construction is used in order to avoid the provision of seals between the valve and the electromagnets.

While We have shown a particular embodiment of our invention, it will be understood, of course, that we do not wish to be limited thereto since many modifications may be made, and we therefore contemplate by the appended claims to cover any such modifications as fall within the true spirit and scope of our invention.

What we claim as new and desire to secure by strips extending radially from a central hub por tion, connections between the ends of said armature and said hub portions, and means securing the ends of said strips to said core member so that saidarmature is normally supported in an unattracted position by said spring strips in axial oating relation with said coil with said annular pole faces respectively in radial and axial spaced relation with the annular pole faces on said core member, said spring strips exerting upon said armature a restoring force which increases with increasing displacement of said armature from said unattracted position. whereby the displacement of said armature is substantially directly proportional to the degree of energizatlon of said coil.

2. The combination in an electromagnet, of a coil, a magnet core member for said coil provided with annular supporting'portions on opposite ends of said coil and with a cylindrical pole face at each end of said coil, a plunger amature extending through said coil, an annu- '50 lar ridge on said amature adjacent each end of said armature provided with a cylindrical peripheral pole face, a support for each end of said armature comprising a disc-like member made of thin spring sheet nonmagnetic material having a plurality of segmental portions cut away to provide at least three spring strips extending radially from a central hub portion to an outer annular portion, connections between the ends of said armature and said hub portions, and means securing the annular portions of each of said supports to said annular portions on said core member whereby said armature is supported by said spring strips centrally of said coil with said annular pole faces respectively in radial spaced relation with the annular pole faces on said core member and biased axially by said spring strips to an unattracted position, each of said strips beingprovided with an arcuate bend giving it increased resiliency for axial movement of said armature when said coil is energized.

3. The combination in an electromagnet, of a coil, a magnet core member for said coil pro vided with cylindrical pole faces at opposite ends of said coil, a plunger armature extending through said coil, an annular ridge on said armature adjacent each end of said armature provided with a cylindrical peripheral pole face, a support for each end of said armature comprising a plurality of spring strips connected to said armature and extending radially from said arman ture, and means securing the ends of said strips to said core member so that said armature is supported by said strips with said annular pole faces respectively in radial spaced relation with the annular pole faces on said core member and biased axially by said spring strips to an unattracted position.

ERWIN R. BOYNTON. WILLIAM T. RAUCH.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,211,768 Schwarzmann Jan. 9, 1917 1,634,292 Lederer July 5, 1927 1,745,878 Trumpler Feb. 4, 1930 2,033,015 Thompson Mar. 3, 1936 2,299,671 White Oct. 20, 1942 FOREIGN PATENTS Number Country Date 97,864 Australia Sept. 10, 1924 

